[PARISC] Fix show_stack() when we can't kmalloc

show_stack() was calling kzalloc() to allocate a struct pt_regs.
This meant that *really* early stack dumps would cause a null pointer
dereference.  x86_64 allocates its pt_regs on the stack, so do the same.

Kyle actually committed this exact patch to CVS on
Wed Jul 26 14:32:39 2006 UTC, and never moved it across to git.
Bad Kyle.
Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>

arch/parisc/kernel/traps.c

@@ -187,18 +187,19 @@ void show_stack(struct task_struct *task, unsigned long *s)
 
 	if (!task) {
 		unsigned long sp;
-		struct pt_regs *r;
 
 HERE:
 		asm volatile ("copy %%r30, %0" : "=r"(sp));
-		r = kzalloc(sizeof(struct pt_regs), GFP_KERNEL);
-		if (!r)
-			return;
-		r->iaoq[0] = (unsigned long)&&HERE;
-		r->gr[2] = (unsigned long)__builtin_return_address(0);
-		r->gr[30] = sp;
-		unwind_frame_init(&info, current, r);
-		kfree(r);
+		{
+			struct pt_regs r;
+
+			memset(&r, 0, sizeof(struct pt_regs));
+			r.iaoq[0] = (unsigned long)&&HERE;
+			r.gr[2] = (unsigned long)__builtin_return_address(0);
+			r.gr[30] = sp;
+
+			unwind_frame_init(&info, current, &r);
+		}
 	} else {
 		unwind_frame_init_from_blocked_task(&info, task);
 	}